Rumbling noise

[georgie2313]

Old Potterton condensing boiler. Started with repetitive high-pitched banging noises in central heating pipework drop-down next to bedroom radiator- then said radiator's TRV valve started leaking. Got radiator replaced. Banging noise resolved. However, that same evening of replacing radiator, roughly 2 hours after having central heating on (no problems if just hot water on), loud rumbling noise in, I think pipework just above hot water tank. Sounds like someone moving heavy furniture across a hard floor. Lasts only a couple of seconds each time. No noise on powering on. All quiet for first 2 hours of heating on, then said noise every 15-30 or so minutes. Heating and hot water hot and radiators all bled. Any idea of the cause? Thank you very much.

 

[Agile]

What does the plumber who replaced the radiator say?

 

[georgie2313]

Plumber tried to fob me off saying its just more noticeable as loft hatch open. But it is a REAL change (loft door closed now!!). I can't trust the plumber unfortunately. When I first told them about original banging noise the reply I got was "That's strange" and no further questions or comments. Basically, I'm being fobbed off!